Based on the implications of sustainable development and the system coordination theories, and from the perspectives of regional resources, the ecological environment, the level of water resources development and utilization, and economic-social development coupling of joint support for the water resources system, we used the pressure-state-response(PSR)model to establish a comprehensive evaluation index system for regional water resources. With reference to previous studies, we put forward the concepts of the sustainable degree and coordinated degree of regional water resources systems and a method for quantitative characterization. On this basis, we propose a comprehensive evaluation method for water resources systems. We carried out an empirical analysis of the security of water resources in Liaoning Province during the period from 2003 to 2013 according to related data. The results are as follows: (1)During the study period, the sustainable degree of the water resources system in Liaoning Province exhibited a rising trend on the whole. The sustainable degree of the resources sub-system showed an unsteady change due to natural factors, and those of the other three sub-systems showed an increasing trend year by year. (2)The coordinated degree of the water resources system of Liaoning Province fluctuated during the study period. The regional resources, ecological environment, level of water resources development and utilization, and economic-social development coupling led to an unstable coordinated relation between the sub-systems. (3)The security level of the water resources system of Liaoning Province increased gradually during the study period, and the security state improved as well. In the future, relevant departments should strengthen the protection of natural resources and the eco-environment, improve the level of water resources exploitation and utilization, and promote regional economic and social development. Besides, exploring new thoughts and methods for coordinated development and unified management of water resources, and involving water resources in regional sustainable development for comprehensive management and optimizing allocation may help to achieve the goal of coordinated and sustainable development of the regional water resources system.